Stator assembly for a brushless motor in a power tool

ABSTRACT

A stator assembly for a brushless DC motor includes a stator core including stator poles and an outer surface, at least one magnet wire wound on the poles forming stator windings, and a bus bar including a non-conductive mount arranged on the outer surface and conductive terminals. Each conductive terminal includes: a main portion mounted on the non-conductive mount substantially parallel to the longitudinal axis of the motor, a tang portion folded over the main portion from a first longitudinal end of the main portion, and a connection tab at a second longitudinal end of the main portion. At least a contact portion of the at least one magnet wire is wrapped around the tang portion and fused to make an electric connection to the conductive terminal, and the connection tab makes electric contact with a wire supplying electric power to the motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/484,595 filed Sep. 24, 2021, which is a continuation of U.S.application Ser. No. 16/689,269 filed Nov. 20, 2019, now U.S. Pat. No.11,133,720, which is a continuation of U.S. application Ser. No.15/783,435, filed Oct. 13, 2017, now U.S. Pat. No. 10,523,080, which isa continuation of U.S. application Ser. No. 13/919,352, filed on Jun.17, 2013, now U.S. Pat. No. 9,819,241, which claims the benefit of U.S.Provisional Application No. 61/660,335, filed Jun. 15, 2012, and is acontinuation-in-part (CIP) of U.S. patent application Ser. No.13/704,033, now U.S. Pat. No. 10,056,806, which is a 35 USC 371 U.S.Nation Stage of PCT Application No. PCT/US2011/040306 filed Jun. 14,2011, which claims the benefit of U.S. Provisional Application Nos.61/354,537, filed Jun. 14, 2010, and U.S. Provisional Application No.61/354,543, filed Jun. 14, 2010. Contents of all said applications areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This disclosure relates to a power tool, and more particularly to astator assembly for an electric brushless DC motor for a power tool.

BACKGROUND

The use of cordless power tools has increased dramatically in recentyears. Cordless power tools provide the ease of a power assisted toolwith the convenience of cordless operation. Conventionally, cordlesstools have been driven by Permanent Magnet (PM) brushed motors thatreceive DC power from a battery assembly or converted AC power. Themotor associated with a cordless tool has a direct impact on many of theoperating characteristics of the tool, such as output torque, timeduration of operation between charges and durability of the tool. Thetorque output relates to the capability of the power tool to operateunder greater loads without stalling. The time duration of the powertool operation is strongly affected by the energy efficiency of themotor. Since, during some operating modes cordless tools are powered bybattery modules that contain a limited amount of energy, the greater theenergy efficiency of the motor, the longer the time duration that thetool can be operated. The durability of a power tool is affected by manyfactors, including the type of motor that is used to convert electricalpower into mechanical power.

Brushed motors such as the PM brushed motors that are generally employedin power tool applications are susceptible to damaged brushes over time.The main mechanical characteristic that separates Permanent Magnetbrushless motors from Permanent Magnet brushed motors is the method ofcommutation. In a PM brushed motor, commutation is achieved mechanicallyvia a commutator and a brush system. Whereas, in a brushless DC motor,commutation is achieved electronically by controlling the flow ofcurrent to the stator windings. A brushless DC motor includes a rotorfor providing rotational energy and a stator for supplying a magneticfield that drives the rotor. Comprising the rotor is a shaft supportedby a bearing set on each end and encircled by a permanent magnet (PM)that generates a magnetic field. The stator core includes field windingsaround the rotor. Power devices such as MOSFETs are connected in serieswith each winding to enable power to be selectively applied. When poweris applied to a winding, the resulting current in the winding generatesa magnetic field that couples to the rotor. The magnetic fieldassociated with the PM in the rotor assembly attempts to align itselfwith the stator generated magnetic field resulting in rotationalmovement of the rotor. A control circuit sequentially activates theindividual stator coils so that the PM attached to the rotorcontinuously chases the advancing magnetic field generated by the statorwindings. A set of sense magnets coupled to the PMs in the rotorassembly are sensed by a sensor, such as a Hall Effect sensor, toidentify the current position of the rotor assembly. Proper timing ofthe commutation sequence is maintained by monitoring sensors mounted onthe rotor shaft or detecting magnetic field peaks or nulls associatedwith the PM.

A brushless motor provides many advantages over conventional brushedmotors. Conventional brushed motors are substantially less durable thanbrushless motors because of the wear and tear associated with thebrushes. Also, since commutation is handled via a microcontroller,mechanical failures associated with the commutation are minimized andfail conditions are better managed and handled. Furthermore, brushedmotors are less efficient than brushless motors due to the friction andthe heat associated with the brushes and the commutator. Brushlessmotors also have the potential to provide size advantages over brushedmotors with similar output levels. Since there is no commutator andbrush system present in a brushless motor, the length of the rotor maybe reduced significantly. The challenge is to efficiently design themotor to similarly reduce the length of the stator assembly. The overallreduction is the length of the motor is particularly useful in compacthandheld power tool applications.

SUMMARY

According to an embodiment of the invention, a power tool is provided.The power tool may be, for example, a drill or an impact driver,although other types of power tools may also be used. The power toolincludes a housing and a motor, such as a brushless DC motor, housedinside the housing. The motor includes a stator assembly and a rotorpivotably arranged inside the stator.

According to an embodiment, the stator assembly includes a laminationstack defining a plurality of poles, field windings each arranged at atleast two opposite poles and connected together around the statorassembly, and a bus bar longitudinally arranged along an outer surfaceof the lamination stack. In an embodiment, the bus bar includesconductive terminals electrically coupled to the field windings and apower source.

According to an embodiment, the stator assembly further includes an endinsulator arranged at a longitudinal end of the lamination stack. Theend insulator may include an extension portion extending longitudinallyover an outer surface of the lamination stack and vertical wallsextending from the extension portion, the vertical walls and theextension portion defining insulating channels for retention of theconductive terminals. Alternatively, the end insulator may include atleast one retaining wall protruding longitudinally along the outersurface of the lamination stack to retain the bus bar. In an embodiment,the stator assembly further includes a second end insulator arranged ata second longitudinal end of the lamination stack, the two endinsulators having retaining features that mate to retain the bus bar. Inan embodiment, the end insulator includes routing features for routingthe wires from the field coils to the bus bar.

According to an embodiment, the bus bar includes a non-conductive mountmounted over the outer surface of the lamination stack, the conductiveterminals being mounted on the non-conductive mount.

According to an embodiment, each conductive terminal includes: a firstplanar portion arranged parallel to the outer surface of the laminationstack and including a first hook extending from a surface thereofarranged to receive a first wire coupled to the field windings; and asecond planer portion arranged at an angle with respect to the firstplaner portion and including a second hook extending from a surfacethereon arranged to receive a second wire coupled to the power source.

According to an embodiment, each conductive terminal includes a tangarranged at a first distal end of the conductive terminal arranged toreceive a first wire coupled to the field windings; and a protruding tabarranged at an angle from a second distal end of the conductive terminalarranged to be connected to a second wire coupled to the power source.In an embodiment, the first wire is wrapped around the tang and fused,and the second wire is welded or soldered to the protruding tab.

According to an embodiment, the field windings are connected to eachother and to the plurality of conductive terminals in at least one of aseries wye, series delta, parallel wye, or parallel deltaconfigurations.

According to an embodiment, field windings are formed from a single wireboth ends of which terminate at one of the conductive terminals.

According to an embodiment of the invention, the stator assemblyincludes a lamination stack defining poles; field windings arranged atat least two opposite poles of said plurality of poles and connectedtogether around the stator assembly; and conductive terminalslongitudinally arranged along an outer surface of the lamination stackand electrically coupled to the plurality of field windings and a powersource.

According to an embodiment, the stator assembly further includes an endinsulator arranged at a longitudinal end of the lamination stack. Theend insulator may include an extension portion extending longitudinallyover an outer surface of the lamination stack and vertical wallsextending from the extension portion, the vertical walls and theextension portion defining insulating channels for retention of theconductive terminals. In an embodiment, the end insulator includesretaining walls protruding longitudinally along the outer surface of thelamination stack to retain the conductive terminals. In an embodiment,the stator assembly includes a second end insulator arranged at a secondlongitudinal end of the lamination stack, the two end insulators havingretaining features that mate to retain the conductive terminals.

According to an embodiment, the stator assembly includes anon-conductive mount mounted over the outer surface of the laminationstack, the conductive terminals being mounted on the non-conductivemount.

According to an embodiment, each conductive terminal includes: a firstplanar portion arranged parallel to the outer surface of the laminationstack and including a first hook extending from a surface thereofarranged to receive a first wire coupled to the field windings; and asecond planer portion arranged at an angle with respect to the firstplaner portion and including a second hook extending from a surfacethereon arranged to receive a second wire coupled to the power source.

According to an embodiment, each conductive terminal includes a tangarranged at a first distal end of the conductive terminal arranged toreceive a first wire coupled to the field windings; and a protruding tabarranged at an angle from a second distal end of the conductive terminalarranged to be connected to a second wire coupled to the power source.The first wire may be wrapped around the tang and fused and the secondwire welded or soldered to the tang.

According to an embodiment, the conductive terminals are distanced fromone another and spread around a periphery of the stator laminationstack.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of this disclosure in any way:

FIG. 1 depicts a perspective cross-sectional view of a power tool,according to an embodiment of this disclosure;

FIGS. 2A and 2B depict perspectives expanded views of a brushlesselectric motor, according to an embodiment of this disclosure;

FIG. 2C depicts a perspective cross-sectional view of the brushlesselectric motor of FIGS. 2A and 2B, according to an embodiment of thisdisclosure;

FIGS. 3A-3C depict various configurations for connecting stator windingsof a brushless motor;

FIG. 4 depicts an exemplary speed-torque diagram of a brushless motorwith different stator winding configurations;

FIGS. 5A and 5B depict a motor stator connected to achieve a deltaconfiguration, according to an embodiment of the invention;

FIG. 5C depicts the bus bar connection of a stator assembly, accordingto an embodiment of the invention;

FIGS. 5D-5H depict conductive plates of the bus bar of FIG. 5C and wireconnections thereto, according to an embodiment of the invention;

FIG. 6 depicts a perspective view of a bus bar of a stator assembly,according to an alternative embodiment;

FIG. 7 depicts a perspective view of the bus bar of FIG. 6 , accordingto an embodiment;

FIG. 8 depicts a partial cross-sectional view of a power tool and motorhaving the stator assembly of FIG. 6 , according to an embodiment;

FIG. 9 depicts a perspective view of a stator assembly including toothdamper inserts, according to an embodiment;

FIG. 10 depicts a cross-sectional view of the stator assembly with thetooth damper inserts inserted between the stator teeth, according to anembodiment;

FIG. 11 depicts an expanded view of the stator assembly showing both thetooth damper inserts of FIG. 9 and the bus bar of FIG. 6 ;

FIG. 12 depicts a perspective view of a stator assembly having a ring oftooth damper inserts, according to an alternative embodiment;

FIG. 13 depicts a perspective view of the stator assembly of FIG. 12with the ring of tooth damper inserts being fully inserted, according toan embodiment.

DESCRIPTION

With reference to the FIG. 1 , a power tool 100 constructed inaccordance with the teachings of the present disclosure is illustratedin a longitudinal cross-section view. The power tool 100 in theparticular example provided may be a drill/driver, but it will beappreciated that the teachings of this disclosure is merely exemplaryand the power tool of this invention could be a circular saw, areciprocating saw, or any similar portable power tool constructed inaccordance with the teachings of this disclosure. Moreover, the outputof the power tool driven (at least partly) by a transmission constructedin accordance with the teachings of this disclosure need not be in arotary direction.

The power tool shown in FIG. 1 may include a housing assembly 102, amotor assembly 104, a control module 104, a battery pack 108, an inputunit (e.g., a variable speed trigger) 110, a transmission assembly 114,an output spindle (not shown), and a chuck (not shown) that can becoupled for rotation with the output spindle. The housing assembly 102can include a housing 102 a and a gear case 102 b that can be removablycoupled to the housing 102 a. The housing 102 a can define a housingbody and a handle 112.

According to an embodiment, the motor 104 is received in the housing 102a. The motor can be any type of motor and may be powered by anappropriate power source (electricity, pneumatic power, hydraulicpower). In the particular example provided, the motor is a brushless DCelectric motor and is powered by a battery pack 108. An input unit 110is mounted in the handle 112 below the housing 102 a. The input unit 110may be a variable speed trigger switch, although other input means suchas a touch-sensor, a capacitive-sensor, a speed dial, etc. may also beutilized. In an embodiment, variable speed trigger switch may integratethe ON/OFF, Forward/Reverse, and variable-speed functionalities into asingle unit and provide respective inputs of these functions to thecontrol unit 106. The control unit 106, which is coupled to the inputunit 110 as described further below, supplies the drive signals to themotor. In the exemplary embodiment of the invention, the control unit106 is provided in the handle 112.

The brushless motor 104 depicted in FIG. 1 is commutated electronicallyby the control unit 106. The tool 100 is powered by a suitable powersource such as the battery pack 108. It is envisioned, however, that thepresent disclosures can be applied to a power tool with an AC powersource, which may further include an AC-to-DC converter to power tomotor. Using the variable-speed input and other inputs from the inputunit 110, the control unit 106 controls the amount of power supplied tothe motor 104. In an exemplary embodiment, the control unit 106 controlsthe Pulse Width Modulation (PWM) duty cycle of the DC power supplied tothe motor 104.

Referring now to FIGS. 2A and 2B, perspectives expanded views of thebrushless electric motor 104 is depicted according to an embodiment ofthe invention. FIG. 2C depicts a cross-sectional view of the brushlessmotor 104. As shown in these figures, in an exemplary embodiment, thebrushless motor 104 includes Hall board mount assembly 210, a statorassembly 230, a rotor assembly 250, and a ring gear mount 270.

The Hall board assembly includes a Hall board mount 212 and a Hall board214. The Hall board 214 snaps onto the Hall board mount 212 via aplurality of pins 216, which may then be welded over the Hall board 214.The Hall board mount 212 includes a bearing support 218 that receives anend bearing 252 of the rotor assembly 250. Mounted on the Hall board 214are one or more Hall Effect sensors 220 arranged around thecircumference of the bearing support 218. The Hall board mount 212further includes a Hall Effect Sensor interference 222 that is coupledto the control unit 106 to provide the control unit 106 with Hall Effectsense signals.

The stator assembly 230 includes a stator 240 having a plurality ofstator windings 232 housed in a stator lamination stack 242. In asix-pole three-phase brushless electric motor, as shown in thisexemplary embodiment, three stator windings 232 are provided within thelamination stack 242. Each stator winding 232 is distributed around thelamination stack 242 to form an even number of poles. In a six-polestator, each stator winding 232 includes a pair of windings arranged atopposite ends of the lamination stack 242 to face each other. The statorwindings 232 may be connected in a variety of configurations. Exemplaryconfigurations include a series delta configuration, a parallel deltaconfiguration, a series wye configuration, and a parallel wyeconfiguration. The distinguishing characteristics of theseconfigurations will be discussed later in detail. The stator assembly230 further includes a bus bar 234 coupled to the control unit 106 toreceive DC power from the control unit 106 to power the field windings232. Using the bus bar 234 and based on the input from the Hall Effectsensors 218, the control unit 106 sequentially commutates the statorwindings 232 to drive the rotor 254. In addition, the stator assembly230 includes a baffle 236 coupled to the stator 240 via snaps or pins238. The baffle 235 may include a protrusion 236 a at its low end tocontain the wiring connections from the bus bar 234 to the statorwindings 232. Alternatively, the baffle 235 may itself integrallyinclude the bus bar 234 to input power from the control unit 106.

In an embodiment, the stator assembly 230 includes alignment features,i.e., pins 310 and receptacles 302, that mate with correspondingalignment features 304, 306 provided on the Hall board mount assembly210 and ring gear mount 270.

FIGS. 3A-3C show different stator windings 232 connections used toachieve the series wye (“Y” shaped) (FIG. 3A), series delta (FIG. 3B),and parallel delta (FIG. 3C) configurations. A parallel wyeconfiguration may also be achieved, although such configuration is notexplicitly shown. The three stator windings in a six-pole brushlessmotor are typically designated as U-U₁; V-V₁; and W-W₁ windings, whereeach winding includes two poles (U and U₁, for example, designate twopoles of the same winding). The wye configuration, sometimes called astar winding, connects all of the windings to a neutral (e.g., ground)point and power is applied to the remaining end of each winding. Thedelta configuration connects the three windings to each other in atriangle-like circuit, and power is applied at each of the connections.For a given motor, the delta configuration achieves higher speed (rpm)at lower torque, whereas the wye configuration achieves relativelyhigher torque at lower speed. The parallel delta configuration achievesthe even higher speed at lower torque load. FIG. 4 depicts an exemplaryspeed-torque diagram of a brushless motor having these configurations.

In a typical off-the-shelf stator assembly for an electric brushlessmotor, the poles of each stator windings 232 (i.e., U and U₁, V and V₁,and W and W₁) are arranged opposite one another and are wound using asingle wire during the manufacturing process. Specifically, the statorhousing typically includes pre-routed wiring connections that connectsterminals 2 (U) and 7 (U), terminal 4 (V) and 9 (V₁), and terminals 6(W) and 11 (W₁) around or adjacent to the stator lamination stack 242(See FIG. 5A). The remaining terminals may then be wired to achieve thedesired configuration, i.e., delta or wye, in series or in parallel.

Conventionally, in a six-pole motor, three adjacent poles are designatedas U, V, and W, opposite the corresponding U₁, V₁, and W₁ poles of thesame winding 232. FIG. 5A depicts the brushless motor 104 with thisarrangement. A challenge with this arrangement, however, is thatterminals 1 (U) and 12 (W₁), terminals 5 (W) and 10 (V₁) and terminals 3(V) and 8(U₁) must be wired together to obtain the delta configuration.It is easy to wire terminals 1 and 12 to each other, as they are locatedadjacent to one another. However, connecting terminals 5 and 10 andterminals 3 and 8 require wiring around the circumference of the stator240. Furthermore, some conventional designs utilize a printed circuitboard attached to the stator to facilitate the connections between thestator terminals, but the copper tracks of the printed circuit board aretypically insufficient in handling large amounts of current in heavyduty power tool applications, such as drills or other high torque powertools.

In order to overcome this challenge, according to an alternativeembodiment of the invention shown in FIG. 5B, the poles of the statorwindings are designated such that the terminals required for wiring adelta connection are arranged adjacent to one another. For example, inan exemplary embodiment, the designation of the stator windings poles Vand V₁ are switched such that terminals 5 and 10 as well as terminals 3and 8 fall adjacent to one another. Accordingly, the terminals can beconnected easily without the need for extra wiring through the center oraround the circumference of the stator 240. The stator windings 232 canbe comprised of one continuous coil tapped at three connection points502 a, 502 b, 502 c for connecting the stator windings 232 to the busbar 234. This arrangement significantly simplifies the motor windingprocess.

FIGS. 5C-5H depict the details of the bus bar 234 and the wiring of thestator assembly 230, according to an embodiment of the invention.

As shown in FIG. 5C, the stator 240 includes the lamination stack 242and end insulators 550, 552. The bus bar 234 includes at least threeinput terminals 502 corresponding to each of the stator windings U, Vand W. In an exemplary embodiment, the input terminals 502 compriseconductive plates 504 separated by insulating channels 506. Theinsulating channels 506, in an embodiment, are formed by a longitudinalextension portion extending over the outer surface of the laminationstack 242, and retaining walls extending vertically from the extensionportion. The extension portions and the retaining walls are formed withthe end insulators 550, 552 and are mated together over the outersurface of the lamination stack 242 to form the insulating channels 506.The bus bar 234 is arranged on an outer periphery of the statorlamination stack 242 and the conductive plates 502 are longitudinallyarranged along the outer periphery of the stator lamination stack 242.The conductive plates 504 may be made of, for example, brass material orother conductive metal. As shown in FIG. 5D, each conductive plate 504may include one or more barb features 512, 514 for attaching theconductive plates 504 inside the insulating channels 506. Further, asshown in FIGS. 5C and 5E, each conductive plate 504 may include a firstplanar portion arranged inside the insulating channels 506 and a secondarranged at an angle from the first planar portion. The conductiveplates include hooks 516 for routing wires from the stator windings tothe conductive plates 504 extending from the first planar portions. Theconductive plate 504 may also include hooks 518 for accommodating thewires from the control unit 106 to the conductive plates 504 extendingfrom the second planar portions.

As shown in FIG. 5F, the barb features 514 of the conductive plates 504snap into corresponding receiving slots 524 inside the insulatingchannels 506. The insulating channels 506 are shown in this figurewithout the walls separating the channels 506. Further, as shown incross-sectional view of FIG. 5G, the barb features 512 engageprotrusions 522 of the insulating channels 506 to lock the conductiveplates 504 within the insulating channels 504. Wires 530 from thecontrol unit 106 may be soldered or attached by other means inside thehooks 518. Similarly, wires 532 from the stator windings 232 may besoldered or otherwise attached inside the hooks 516. FIG. 5H depicts anexpanded view of the stator assembly 230 including the wires 532 leadingfrom the stator windings 232 and through the insulating channels 506into the hooks 516.

The above-described embodiment of the bus bar 234 provides severaladvantages. First, since the terminals (i.e., conductive plates 504) areprovided on the outer surface of the stator lamination stack, noadditional space is taken up longitudinally. This reduces the overalllength of the stator assembly. Also, the insulating channels that retainthe terminals are molded as a part of the end insulators 550, 552, whichsignificantly eases the manufacturing process.

In the above-discussed embodiment, during the course of motormanufacturing, the ends of the stator magnet wires are stripped of wireinsulation and paired together. The pairs of leads are then receivedinside corresponding hooks 516 of conductive plates 504, and the hooksare crimped and soldered to the wire leads. The power inputs from thecontrol unit and power source are similarly connected to the othercorresponding hooks 518 of the conductive plates 504. While thisarrangement may be desirable in some applications, the stripping andcrimping steps may pose challenges during the motor manufacturingprocess.

FIGS. 6-8 depict an alternative and improved bus bar 334, according toan alternative embodiment of the invention. FIG. 6 shows a statorassembly 340 including the bus bar 334, according to this embodiment.FIG. 7 shows a perspective view of the bus bar 334. FIG. 8 illustrates across-sectional view of the stator assembly 340 including the bus bar334 inside a power tool housing.

In this embodiment, the bus bar 334 is arranged on an outer surface ofthe stator lamination stack 242. The bus bar 334 may extend fully orpartially along the outer surface (i.e., outer periphery) of the statorlamination stack 242. The bus bar 334 includes three terminals (alsoreferred to as conducive terminals or conductive plates) 604 arrangedlongitudinally along the outer surface of the lamination stack 242. Inan embodiment, the conductive plates 604 are mounted on a non-conductivemount 602. The conductive plates 604 are separated and insulated fromeach other via the mount 602. The mount 602 is mounted on the outersurface of the lamination stack 242. The end insulators 650 and 652,which are arranged at the longitudinal ends of the lamination stack 242,are provided with retaining walls 651 and 653, respectively, which matetogether over the outer surface of the lamination stack 242 around themount 602 to retain the mount 602 over the outer surface of thelamination stack 242.

Conductive plates 604 in this embodiment include connection tabs 618arranged at a first longitudinal distal end in the proximity of the endinsulator 650, and tangs 616 arranged at a second longitudinal distalend in the proximity of the end insulator 652. The tangs 616 fold backover a main surface of the conductive plates 604 in the longitudinaldirection of the conductive plates 604. The stator magnet wire 620,which is wound around the lamination stack slots to form stator coils,are routed over the end insulator 652 between the coils to connect thecoils in wye or delta configurations. The end insulator 652 may beprovided with routing features for routing and positioning the wire 620.In an embodiment, the magnet wire 620 may be wrapped around the tangs616 at various points, e.g., either at the wire leads or at mid points,to facilitate the desired winding configuration. For example, for adelta connection (see FIG. 3B), the magnet wire 620 may be first wrappedaround a first tang 616 at a lead end, routed and wound to form coils Wand W1, wrapped around a second tang 616, routed and wound to form coilsU and U1, wrapped round a third tang 616, routed and wound to form coilsV and V1, and terminated at the first tang 616. The fusing process burnsa portion of the magnet wire insulation material that is in contact withthe tangs 616. The fusing step thus eliminates the need for strippingthe contact portion of the magnet wires. In an embodiment, the tangs 616may be pressed over the magnet wire contact portion.

Connection tabs 618 project outwardly from the bus bar 334 and thestator lamination stack 242. Each tab 618 may include a through-holetherein. The motor wires (not shown) received from the control unit,which carry electric power to the motor field windings, may be insertedinto the through-holes of the corresponding tabs 618 and soldered.Alternatively, the motor wires may be welded to the connection tabs 618.In yet another embodiment, additional terminals 660, as shown in FIG. 8, may be welded to the connection tabs 618.

The aforementioned embodiment offers several advantages. For example,the tang 616 geometry of the bus bar 334 may be designed to accommodateany amount of wire 620 leads and wire diameter. Also, the bus bar 334may be designed to accommodate any lamination stack 242 length. Thefusing of the stator magnet wires and attaching the motor wires alsobecomes easier using this embodiment. It must be noted that while themount 602 is shown as a separate piece, the end insulators 650 and 652may be provided with features to integrally form the mount 602. Also,the end insulators 650 and 652 may be provided with retaining featuresto support and retain the conductive plates 604 at various locationsaround the outer periphery of the stator assembly, e.g., at 120 degreeangles.

Another aspect of this disclosure is discussed herein with continuedreference to FIGS. 2A and 2B, and further in reference to FIGS. 9-12 .It was found that many brushless motors platform, such as, for example,those using the stator assembly depicted in FIGS. 2A and 2B, develop aresonating frequency that is unpleasant to the end user when used inhigh-speed and/or high-power applications such as high speed powertools. The inventors of this application found that this noise isattributable to the stator laminations flexing and distorting at highspeed. Specifically, as the rotor 250 rotates inside the stator assembly230, the magnetic force of the rotor 250 magnets cause a small amount ofvibration in the stator lamination poles. It was initially believed thatthe noise is generated by small movements of the individual laminationswith respect to one another. However, it was found that reinforcing thelaminations with respect to one another via adhesive or other means doesnot reduce the noise. The inventor then found that the lateral vibrationof the poles and the pole teeth is primarily responsible for the noise.One solution is to increase the thickness of the lamination stack behindeach pole. The reinforced metal behind each pole reduces the amount ofunwanted vibration. However, increasing the thickness of the laminationstack increases the overall motor size, which is undesirable in manypower tool applications.

In order to reduce the noise from the lamination stack poles and poleteeth, according to an embodiment on this disclosure, non-conductivetooth damper inserts may be provided inside the lamination stack slotsto provide further support for the laminations teeth, as shown in FIGS.9-13 . In one embodiment, as shown in FIGS. 9 and 10 , the tooth damperinserts 920 are provided within each slot 904 of the stator assembly 340extending in a direction of the center of the stator assembly 340. FIG.9 illustrates a perspective view of the stator assembly 340, with thetooth damper inserts 920 pulled out of the slots 904 for a better view.FIG. 10 illustrates a cross-sectional view of the stator assembly 340,with the tooth damper inserts 920 inserted in to the slots 904.

In an embodiment, each tooth damper insert 920 may include two radialend portions. A radial outer end 924 engages an outer wall of the slot904 defined by an inner surface of the stator assembly 340, i.e., theinner surface of the lamination stack 242 and/or the slot wall portionsof the end insulators 650 and 652 at the back of the slot 904. Theradial outer end 924 may have an arcuate shape following a profile ofthe outer wall of the slot 904. The radial outer end 924 providessupport for the laminations against radial movement and vibration.

In an embodiment, a radial inner end of the tooth damper insert 920 isarranged at an open end of the slot 904 formed between adjacent statorteeth 906 and engages lateral edges of the opposing teeth 906 thatdefine the open end of the slot 904. In an embodiment, the second endportion includes two side projections (i.e., notches) 922 that engageback edges of the teeth 906. The second end portion of the tooth damperinsert helps support the laminations teeth against rotational and/orradial movement and vibration. In an embodiment, the tooth damperinserts 920 are inserted into the slots 904 after the stator assembly340 is fully wound. In an embodiment, the radial inner end of the toothdamper inserts 920 and the stator teeth 906 are aligned along a circle.

FIG. 11 depicts an expanded view of the stator assembly 340, includingthe tooth damper inserts 920, stator field windings 902, magnet wires620, stator lamination stack 242, end insulators 650 and 652, and thebus bar 334, according to an embodiment of the invention. The endinsulators 650 and 652 are shown with walls 251 and 253 that matetogether to securely hold the bus bar 334. The end insulators 650 and652 are also shown with slot walls 650 a and 652 a that tightlypenetrate into the slots of the lamination stack 242. The slot walls 650a and 652 a support to the tooth damper inserts 920 inside the slots904. In an embodiment, each of the slot walls 650 a and 652 a extendswithin the interior of the slot 604 from one tooth 906 to another. In anembodiment, the lateral edges of each slot wall 650 a and 652 a arepositioned in the proximity of the inner edges of the teeth 906 so as tobe in contact with (or close to) notches 922 of the tooth damper inserts920. This allows the tooth damper inserts 920 notches 922 to engage themetallic edges of the teeth 906.

FIGS. 12 and 13 depict teeth damper inserts pre-assembled into a ring950, according to an embodiment. In this embodiment, the tooth damperinserts are pre-assembled into a ring 950 prior to insertion into thelamination stack slots. The ring 950 may include an outer ring 954 andan inner ring 956, with an upper surface of the tooth damper insertsextending from the outer ring 954 to the inner ring 952. The ring 950includes through-holes corresponding to the stator coils 902 formedbetween the tooth damper inserts. The ring 950 may also includeretention features 958 corresponding to snaps 915 provided on the endinsulator 650. The ring 950 in this embodiment provides support for thetooth damper inserts. Additionally, the integrated ring 950 enablesinsertion of the tooth damper inserts in a single step, thus improvingthe assembly process.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the scope of the invention.

The invention claimed is:
 1. A power tool comprising: a housingincluding a motor housing and a handle portion; a motor control unitdisposed within the handle portion; a transmission assembly mountedforward of the motor housing; and a motor housed inside the motorhousing, the motor having a stator assembly and a rotor rotatablyarranged inside the stator, the stator assembly comprising: a statorcore defining a plurality of poles and having an outer surface that issubstantially cylindrical formed around a longitudinal axis of themotor; at least one magnet wire wound on the plurality of poles forminga plurality of stator windings; and a bus bar comprising: anon-conductive mount arranged on the outer surface of the stator core,and a plurality of conductive terminals arranged to receive electricpower from a power source and supply electric power to a plurality ofphases, wherein each of the conductive terminals includes: a mainportion at least partially mounted on the non-conductive mount, a tangportion extending angularly from a first longitudinal end of the mainportion, and a connection tab extending angularly from a secondlongitudinal end of the main portion, wherein the first longitudinal endof the main portion is rearward of the second longitudinal end relativeto the transmission assembly, at least a contact portion of the at leastone magnet wire is wrapped around the tang portion and fused to make anelectric connection to the conductive terminal, and the connection tabis arranged to makes electric contact with a power wire supplyingelectric power to the motor, wherein the power wire is received from themotor control unit through the handle portion and connects to theconnection tab without traversing rearwardly past the secondlongitudinal end of the main portion.
 2. The power tool of claim 1,wherein the stator assembly further comprises an end insulator arrangedat a longitudinal end of the stator core.
 3. The power tool of claim 2,wherein the end insulator comprises an extension portion extendinglongitudinally over an outer surface of the stator core to retain thebus bar on the outer surface of the stator core.
 4. The power tool ofclaim 2, wherein the end insulator comprises two retaining wallsprotruding longitudinally along the outer surface of the stator core ontwo sides of the bus bar to retain the bus bar on the outer surface ofthe stator core.
 5. The power tool of claim 2, wherein the statorassembly further comprises a second end insulator arranged at a secondlongitudinal end of the stator core, the two end insulators havingretaining features that mate to retain the bus bar on the outer surfaceof the stator core.
 6. The power tool of claim 1, wherein the conductiveterminals are arranged at close proximity to one another in parallel,and the non-conductive mount electrically isolates the plurality ofconductive terminals.
 7. The power tool of claim 1, wherein theconnection tab protrudes at an approximately perpendicular angle fromthe second longitudinal end of the main portion and includes a hole forreceiving the power wire.
 8. The power tool of claim 1, wherein thepower wire is soldered to the connection tab.
 9. The power tool of claim1, wherein the tang portion is pressed over a portion of the contactportion of the at least one magnet wire.
 10. The power tool of claim 1,wherein two ends of the at least one magnet wire terminate around thetang portion of one of the plurality of terminals.